一感（feel）、二听（hear, listen to）、三让（let, make, have）、四看（look at, see, watch, notice）。但变被动语态时，必须加上to。如：
My friends were made to work the whole night by the boss. 4. 不定式作定语
①不定式作定语时，应放在名词之后。它与名词有逻辑上的动宾关系。
②如果是不及物动词，且与所修饰的词之间有动宾关系，要在不定式后加上适当的介词。 There is nothing to worry about. 没有什么可担心的。 5.不定式作状语
表示目的、原因、结果或条件。 I came here to see you . (目的)
We were very excited to hear the news. (原因)
He hurried to the school to find nobody there. (结果)
6.不定式作表语
My job is to help the patient.
7.不定式常和疑问词what, which, when, where, how连用，相当于一个宾语从句。如：The teacher is telling the students what to do. 老师正告诉学生们做什么。 He didn't know where to go. 他不知道去哪里。
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